chore: deleted obsolete plugins

Author: wernerglinka

package.json

@@ -45,7 +45,6 @@
     "metalsmith": "^2.5.1",
     "metalsmith-html-minifier": "^4.0.1",
     "metalsmith-if": "^0.1.1",
-    "metalsmith-metadata": "^0.0.4",
     "metalsmith-prism": "^4.1.0",
     "metalsmith-static-files": "^0.2.0"
   },